Yes, the appearance of the pistils indicates that flowering is about to commence. The plants will not grow a great deal more and growth will be switched to the production of flowers, rather than vegetative growth. Auto flowers are not noted for their size, more so there limited growing cycle before flowering commences.
If you are seeking a better yield, grow normal photo period plants, which will produce much more, with fewer problems, a simplified growing/flowering cycle, all while consuming less electricity to do so.
Hope this helps,...... Organoman.